Messages in this thread | | | From | Dmitry Vyukov <> | Date | Mon, 15 Mar 2021 11:03:30 +0100 | Subject | Re: [PATCH] task_work: kasan: record task_work_add() call stack |
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On Mon, Mar 15, 2021 at 10:38 AM Walter Wu <walter-zh.wu@mediatek.com> wrote: > > On Mon, 2021-03-15 at 07:58 +0100, 'Dmitry Vyukov' via kasan-dev wrote: > > On Mon, Mar 15, 2021 at 3:00 AM Walter Wu <walter-zh.wu@mediatek.com> wrote: > > > > > > Why record task_work_add() call stack? > > > Syzbot reports many use-after-free issues for task_work, see [1]. > > > After see the free stack and the current auxiliary stack, we think > > > they are useless, we don't know where register the work, this work > > > may be the free call stack, so that we miss the root cause and > > > don't solve the use-after-free. > > > > > > Add task_work_add() call stack into KASAN auxiliary stack in > > > order to improve KASAN report. It is useful for programmers > > > to solve use-after-free issues. > > > > > > [1]: https://groups.google.com/g/syzkaller-bugs/search?q=kasan%20use-after-free%20task_work_run > > > > > > Signed-off-by: Walter Wu <walter-zh.wu@mediatek.com> > > > Suggested-by: Dmitry Vyukov <dvyukov@google.com> > > > Cc: Andrey Ryabinin <ryabinin.a.a@gmail.com> > > > Cc: Dmitry Vyukov <dvyukov@google.com> > > > Cc: Andrey Konovalov <andreyknvl@google.com> > > > Cc: Alexander Potapenko <glider@google.com> > > > Cc: Andrew Morton <akpm@linux-foundation.org> > > > Cc: Matthias Brugger <matthias.bgg@gmail.com> > > > Cc: Jens Axboe <axboe@kernel.dk> > > > Cc: Oleg Nesterov <oleg@redhat.com> > > > --- > > > kernel/task_work.c | 3 +++ > > > mm/kasan/kasan.h | 2 +- > > > 2 files changed, 4 insertions(+), 1 deletion(-) > > > > > > diff --git a/kernel/task_work.c b/kernel/task_work.c > > > index 9cde961875c0..f255294377da 100644 > > > --- a/kernel/task_work.c > > > +++ b/kernel/task_work.c > > > @@ -55,6 +55,9 @@ int task_work_add(struct task_struct *task, struct callback_head *work, > > > break; > > > } > > > > > > + /* record the work call stack in order to print it in KASAN reports */ > > > + kasan_record_aux_stack(work); > > > > I think this call should be done _before_ we actually queue the work, > > because this function may operate on non-current task. > > Consider, we queue the work, the other task already executes it and > > triggers use-after-free, now only now we record the stack. > > agree, what do you think below change? > > --- a/kernel/task_work.c > +++ b/kernel/task_work.c > @@ -34,6 +34,9 @@ int task_work_add(struct task_struct *task, struct > callback_head *work, > { > struct callback_head *head; > > + /* record the work call stack in order to print it in KASAN reports > */ > + kasan_record_aux_stack(work); > +
This looks good to me.
> do { > head = READ_ONCE(task->task_works); > if (unlikely(head == &work_exited)) > @@ -55,9 +58,6 @@ int task_work_add(struct task_struct *task, struct > callback_head *work, > break; > } > > - /* record the work call stack in order to print it in KASAN reports > */ > - kasan_record_aux_stack(work); > - > return 0; > } > > > Moreover, I think we can trigger use-after-free here ourselves while > > recording the aux stack. We queued the work, and the work can cause > > own free, so it's not necessary live by now. > > Sorry, I don't fully know your meaning, do you mean we should add an > abort when detect use-after-free?
I meant that where we had the kasan_record_aux_stack(work) call in the first version of the patch, work can be already freed. We must not access work after queueing it.
> > > return 0; > > > } > > > > > > diff --git a/mm/kasan/kasan.h b/mm/kasan/kasan.h > > > index 3436c6bf7c0c..d300fe9415bd 100644 > > > --- a/mm/kasan/kasan.h > > > +++ b/mm/kasan/kasan.h > > > @@ -146,7 +146,7 @@ struct kasan_alloc_meta { > > > struct kasan_track alloc_track; > > > #ifdef CONFIG_KASAN_GENERIC > > > /* > > > - * call_rcu() call stack is stored into struct kasan_alloc_meta. > > > + * Auxiliary stack is stored into struct kasan_alloc_meta. > > > * The free stack is stored into struct kasan_free_meta. > > > */ > > > depot_stack_handle_t aux_stack[2]; > > > -- > > > 2.18.0 > > > > -- > You received this message because you are subscribed to the Google Groups "kasan-dev" group. > To unsubscribe from this group and stop receiving emails from it, send an email to kasan-dev+unsubscribe@googlegroups.com. > To view this discussion on the web visit https://groups.google.com/d/msgid/kasan-dev/1615801102.24887.4.camel%40mtksdccf07.
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